This invention relates to a secondary intake gas control system for a spark-ignition internal combustion engine of a motor vehicle, in which the secondary intake gas inducted into the engine is optimized during warming-up of the engine when a choke valve is operated.
In conventional spark-ignition internal combustion engines of motor vehicles provided with carburetors, firing and burning of an air-fuel mixture are poor during idling or low-speed and light-loaded driving range of the engine, since due to throttling of a throttle valve the efficiency of suction of the mixture into a combustion chamber is poor and the velocity of flow of the mixture is low.
In order to prevent deterioration of said firing and burning of the mixture, it has been proposed to supply a rich air-fuel mixture having a small air-fuel ratio which is easily combustible. Also, it has been known to inject air or other gas into the combustion chamber in a predetermined direction, independently of the air-fuel mixture inducted thereinto, thereby producing a strong swirl of the mixture in the combustion chamber and consequently increasing a velocity of flame propagation. In the latter case, however, it is required to maintain always an air-fuel ratio of the entirety of the mixture and the air or gas in the combustion chamber at an appropriate value. It is also required to control the amount of the mixture to be inducted and the amount of air or gas to be injected so as to produce the strong swirl in said combustion chamber.